1. Field of the Invention
The present invention relates to a sealed secondary battery (typically, a sealed secondary battery that as a whole has an angular shape (rectangular parallelepiped shape). More specifically, the present invention relates to a sealed secondary battery equipped with a current interrupt mechanism actuated by increase in internal pressure.
Note that this application claims priority under the Paris Convention based on Japanese Patent Application No. 2012-015980, filed on Jan. 27, 2012, the entire contents of which are incorporated into this application by reference.
2. Description of the Related Art
Secondary batteries such as lithium secondary batteries and nickel hydride batteries have been advantageously used in recent years as the so-called portable power sources for personal computers or portable terminals, or power sources for vehicles. In particular, lightweight lithium secondary batteries that make it possible to obtain a high energy density are expected to be advantageously used as high-output power sources for driving the vehicles such as electric automobiles and hybrid automobiles.
A battery of a sealed structure (sealed battery) in which an electrode body including a positive electrode and a negative electrode is sealed together with an electrolyte inside a battery case is a typical structural example of such secondary batteries. When a battery of such kind is charged, where a malfunction occurs due to the presence of a defective battery or a failure of a charging device, it can be assumed that an unusually high current will be supplied to the battery and the battery will get into an overcharged state. During such overcharging, battery reactions proceed at a high speed, gas is generated inside the sealed battery case, the internal pressure of the battery case rises, and the case can be deformed by the abnormal internal pressure (gas pressure). In order to resolve this problem, a battery structure has been suggested in the related art that includes a current interrupt mechanism such that a part thereof is deformed by the pressure inside the case (gas pressure) when an abnormality occurs in the battery, and the conductive portion is physically ruptured, thereby interrupting the electric current.
The conventional example relating to a secondary battery equipped with a current interrupt mechanism of such a configuration is disclosed in Japanese Patent Application Publication No. 2010-212034. The current interrupt mechanism disclosed in this publication includes a rectangular plate-shaped current collecting plate connected to an electrode body accommodated inside the case of an angular sealed secondary battery and an inversion plate (current interrupt valve) conductively welded to part of the current collecting plate. When the internal pressure of the case (gas pressure) rises, the inversion plate is inverted and deformed by the gas pressure in the direction of separating from the electrode body and current collecting plate, and part of the collector including the abovementioned welded portion breaks following this deformation. Current interruption is thus realized by such inversion, deformation and separation of the inversion plate from the collector main body.
In the current interrupt mechanism configured as described in Japanese Patent Application Publication No. 2010-212034, the welded portion of the current collecting plate and periphery thereof are formed to be thinner than other portions of the current collecting plate, and/or a groove (notch: cut-out portion) is formed in advance in a zone which is to be broken, so that the inversion plate (current interrupt valve) be inverted and deformed and that part of the collector including the above-mentioned welded portion be rapidly broken when this internal pressure of the case is reached, thereby ensuring that the electric current is reliably interrupted when the internal pressure of the case that has been set in advance (that is, a predetermined gas pressure) is reached.
Sealed secondary batteries used as drive power sources for vehicles such as electric automobiles and hybrid automobiles (including plug-in hybrid automobiles) are required to have a large capacity at a high output (typically a large capacity such that 1-hour-ratio capacity is equal to or greater than 3 Ah, for example, 5 to 20 Ah, or equal to or greater than 20 Ah (for example, 20 to 30 Ah) in order to demonstrate even better performance. Therefore, high-rate charge and discharge are required that are incomparable with that of the batteries used as power sources for personal computers or portable terminals (that is, for consumer applications).